1. Field of the Invention
This invention relates to a rotation support apparatus for a compressor pulley, and more particularly to a compressor pulley support apparatus which is installed for use in the rotation drive apparatus of a compressor for the air-conditioning apparatus of an automobile so as to support a follower pulley at the stationary portion, such as the housing, of the compressor such that the follower pulley can rotate freely for rotation drive of the compressor.
2. Description of the Related Art
The compressor installed in the air-conditioning apparatus of an automobile for compressing refrigerant is rotated by the engine for automobile operation. Therefore, there is an endless belt that runs between the follower pulley that is formed on the end of the rotating shaft of the compressor and the drive pulley that is fastened to the end of the crankshaft of the engine, and the rotating shaft of the compressor is rotated by the rotation of this endless belt.
FIG. 7 shows a construction of the rotation drive section of the rotating shaft 1 of the compressor. This rotating shaft 1 is supported inside a casing 2 by a rolling bearing (not shown in the figure) such that it rotates freely. A follower pulley 4 is rotatably supported around the support cylinder section 3 that is formed on the outer surface on the end of the casing 2, by a multi-row radial ball bearing 5. This follower pulley 4 is entirely ring shaped with a U-shaped cross section, and a solenoid 6 that is fastened to the end surface of the casing 2 is located in the space inside the follower pulley 4.
On the other hand, there is an installation bracket 7 that is fastened on the end of the rotating shaft 1 in the section that protrudes from the casing 2, and a ring-shaped plate 8 that is made of a magnetic material is supported by way of a plate spring 9 around this installation bracket 7. This ring-shaped plate 8 is separated from the follower pulley 4 as shown in FIG. 7 by the elastic force of the plate spring 9 when there is no electric current flowing to the solenoid 6, and it is attracted toward the follower pulley 4 when there is electric current flowing to the solenoid 6, such that rotation force is freely transmitted to the rotating shaft 1 from the follower pulley 4. In other words, the solenoid 6, ring-shaped plate 8 and plate spring 9 form an electromagnetic clutch 10 for engaging and disengaging the follower pulley 4 and rotating shaft 1.
As described above, when the follower pulley 4 is supported by a double-row radial ball bearing 5 such that it rotates freely, and when an eccentric load is slightly applied to the follower pulley 4 from the endless belt 11 that extends around the follower pulley 4, rarely does the center axis of the outer race 12 of the double-row radial ball bearing 5 come out of alignment (become tilted) with the center axis of the inner race 13. Moreover, this construction makes it possible to sufficiently secure the durability of the double-row radial ball bearing 5, as well as prevent tilting of the rotation axis of the follower pulley 4 and eccentric wear of the endless belt 11.
However, by using the double-row radial ball bearing 5, it is impossible to avoid an increase in dimensions in the axial direction. In many cases, the rotation support section for the follower pulley 4 must be located in a limited space, and therefore any increase in dimensions in the axial direction is not preferable. In addition, as the dimensions in the axial direction increase, the cost of component parts also increases.
In the case that a single-row, deep-groove radial ball bearing is used instead of the double-row radial ball bearing 5 as the roller bearing for supporting the follower pulley 4, it becomes easier to reduce the dimensions in the axial direction and to fit the bearing in a limited space. However, in the case of a single-row, deep-groove radial ball bearing, when the follower pulley 4 receives a moment load, the force for preventing tilting of the follower pulley 4 is small so the misalignment of the center axis of the outer race of the radial ball bearing with the center axis of the inner race becomes severe. As a result, durability of the radial ball bearing becomes inadequate and it becomes easy for excessive eccentric wear of the endless belt 11 that extends around the follower pulley 4 to occur.
In consideration of the aforementioned problems, use of a single-row, 4-point contact radial ball bearing for supporting the follower pulley, as disclosed in Japanese Patent Publications Nos. Tokukai Hei 9-119510, and Tolcukai Hei 11-336795, has been known. FIG. 8 and FIG. 9 show a second example of the prior construction as disclosed in Japanese Patent Publication No. Tokukai Hei 9-119510.
In this second example of the prior construction, the follower pulley 4 is made of sheet metal by a bending process such as pressing, and is such that it can be rotatably supported around a support section (not shown in the figure) by a single-row, 4-point contact radial ball bearing 14. This radial ball bearing 14 comprises an outer race 15 and inner race 16, which are concentrically supported, and a plurality of balls 17. Of these, an outer-ring raceway 18 is formed around the inner peripheral surface of the outer race 15, and an inner-ring raceway 19 is formed around the outer peripheral surface of the inner race 16. Both of these raceways 18, 19 have a gothic arch-shaped cross section having a pair of arcs that both have a radius of curvature that is more than xc2xd of the diameter of the balls 17 and intersect each other at the mid portion. Accordingly, the rolling surface of the balls 17 comes into contact with the raceways 18, 19 at two points respectively, so that there are four contact points in total for each of the balls 17.
This kind of 4-point contact type radial ball bearing 14 is more rigid against moment loads than a typical single-row, deep-groove radial bearing, and when a moment load is received, it is very difficult for the center axis of the outer race 15 to come out of alignment with the center axis of the inner race 16. Therefore, it is possible to alleviate eccentric wear to the endless belt 11 (see FIG. 7) that extends around the follower pulley 4 when compared with a pulley rotation support apparatus for a compressor that uses a typical single-row, deep-groove radial ball bearing.
In Japanese Patent Publication No. Tokukai Hei 11-336795, the 4-point contact type radial ball bearing described above is assembled in the rotation support section of the follower pulley for the compressor drive, and furthermore, an electromagnetic clutch is placed between the follower pulley and the rotating shaft of the compressor.
Moreover, as shown in FIG. 10, even in the case of a single-row ball bearing 14 of the 3-point contact type, the rigidity against moment loads is greater than for a typical single-row, deep-groove radial ball bearing, and when a moment load is received, it is difficult for the center axis of the outer race 15 to come out of alignment with the center axis of the inner race 16. This 3-point contact type ball bearing 14 has an inner-ring raceway 19 formed around the outer peripheral surface of the inner race 16 such that its cross section is arc shaped to have a single radius of curvature that comes in contact with the rolling surface of the ball 17 at one point, and a gothic arch-shaped outer-ring raceway 18 formed around the inner peripheral surface of the outer race 15, that comes in contact at two points with the rolling surface of the ball 17 in the same way as the radial ball bearing 14 of the 4-point contact type shown in FIG. 9. In the case of supporting the pulley of a compressor with this kind of 3-point contact ball bearing 14 as well, it is possible to alleviate eccentric wear to the endless belt 11 (see FIG. 7) that extends around the follower pulley 4 when compared with a pulley rotation support apparatus for a compressor that uses a typical single-row, deep-groove radial ball bearing.
In contrast to the construction shown in FIG. 10, a 3-point contact type ball bearing in which the rolling surface of the ball comes in contact with the outer-ring raceway at one point, and the inner-ring raceway at two points, has the same effect.
As mentioned above, in the case of assembling a 3-point contact radial ball bearing or 4-point contact radial ball bearing in the support section for rotatably supporting a follower pulley for the compressor drive, it is possible to sufficiently secure both of the compact size, lightness of weight and the durability of the bearing. However, in these prior art cases, since the dimensions of all parts were not sufficiently examined, it was not always possible to obtain adequate results.
An objective of this invention is to provide a rotation support apparatus for compressor pulley that will solve the problems described above.